Field of the Invention
A solar central receiver system employing common positioning mechanism for heliostats relates to a system of concentrating and harvesting solar energy. The solar central receiver system utilizes arrays of heliostats, wherein each array has a common positioning mechanism for tracking the apparent diurnal movement of the sun for both altitude and azimuth axes. The common positioning mechanism periodically brings about synchronized orientation of heliostats such that the incident solar radiation is continually focused onto a stationary object from dawn to dusk.
Description of the Related Art
Solar energy has received attention as a clean and environment friendly energy. However, the maximum solar energy density is only about 1000 watts/m2 even when the sun irradiates vertically in a fine day. Therefore, for utilization of solar energy, its efficient concentration is required. The popular solar radiation collection and utilization devices are reflector types. A solar central receiver system (solar furnace) is a dependable efficient producer of large commercial quantities of power. Such a system includes reflectors, tracking system for reflectors, an absorber, and a thermal harvesting system.
Generally, a solar furnace has a tower-mounted central receiver for collection of sunlight and conversion thereof into electricity. The solar radiation is concentrated on to the central receiver by reflection from heliostats spaced about the tower. A solar tracking system aims the heliostats by continually predicting the location of the sun in the sky. Predictions are based on the date, time, longitude and latitude. Using the predicted location of the sun and the position of the central receiver with respect to each heliostat (optical element), azimuth and/or elevation angles are periodically calculated for each heliostat and each heliostat is positioned accordingly. Configuring each heliostat to be individually movable typically requires a large amount of expensive motorized equipment. Each heliostat requires dedicated motors for azimuthal and altitudinal tracking. Besides, each heliostat has to be independently supported by a sturdy pedestal for providing the structural strength. While rotating each heliostat for solar tracking, there is usually a mechanical error in precision that cannot be overcome. Even negligible mechanical errors add up and result in inaccurate aiming. Inaccurate aiming may result in spillage and thermal damage to structures and appliances near the central receiver. Increasing the accuracy and efficiency of heliostats by employing expensive aiming devices significantly increases the plant cost.
A need therefore exists to have a low cost and simple but efficient common positioning mechanism for providing altitudinal as well as azimuthal orientation of arrays of heliostats in a solar central receiver system. An objective of the present invention is to install arrays of heliostats that are synchronously rotatable about altitudinal as well as azimuthal axis by a common positioning mechanism such that the heliostats continue to reflect the sunlight towards a stationary object from dawn to dusk. An objective of the present invention is to employ a common positioning mechanism for arrays of heliostats for both altitude and azimuth axis orientation. Consequently, expensive motorized equipments for configuring individual precise positioning of each heliostat for solar tracking would not be needed.
In conventional heliostats, it is essential to individually control rotation of mirror of each heliostat in accordance with the diurnal movement of the sun. This necessitates individual sensing and alignment devices for heliostats, a state of the art computer for predicting and controlling the required altitudinal and azimuthal rotation of each heliostat, and protecting said computer from heat and dust. This results in an increased cost. A need therefore exists to reduce these extensive sensing, alignment and computing operations. Therefore the objective of the present invention is to have a common positioning mechanism, wherein prediction of altitudinal and/or azimuthal rotation of any heliostat would suffice to predict the altitudinal and or azimuthal rotation of the entire respective array of heliostats or all the heliostats of the heliostat field. In the present invention, arrays of heliostats track the sun synchronously, which largely simplifies the control system compared to the conventional multi-dimension tracking equipment. Furthermore, expensive alignment equipment for each optical element (heliostat) and obligatory sturdy pedestal for each optical element could be avoided.
In addition, reflector mirror of a heliostat assembled on a conventional pedestal is like a sail ready to fly off when the wind gets underneath it. The force exerted on reflecting surfaces of heliostats by a gust of wind is large and will be dozens of times larger on the bearing points of the supporting pedestals. Hence it is an objective of the present invention to utilize arrays of heliostats on rotatable shafts and to eliminate the need of individual sturdy pedestals. Being low-level arrays, the heliostats of the present invention are not significantly exposed to wind loads and consequently the structural problems are greatly reduced. The position of heliostats close to the ground has an advantage of reduced wind velocity. Furthermore, packing the heliostats in horizontal plane helps to attenuate the wind force from row to row.
The present invention either eliminates or reduces the required number of motors, gearboxes, hydraulic pistons, hoses, other activators, computing systems and massive supports for the heliostats as is essential for the operation of conventional solar central receiver systems. This advantageously reduces the cost and complexity. Thus, the rationale of the present invention is to provide many advantages and novel features that are not anticipated or implied by any of the prior art.